Why Women Have Sex

While figuring out what women want has stumped men for centuries, understanding how they think about sex may have just gotten easier. Cindy Meston and David Buss, psychologists at the University of Texas, interviewed over 1,000 women around the world for their book Why Women Have Sex and managed to come up with 237 reasons, ranging from the predictable  commitment  to the puzzling  curing a headache. Spoiler alert: love may be further down on the list than one might think. TIME spoke to Buss about the myriad mind games, turn-ons and turn-offs involved in female sexuality, and what a guy can do to stand a chance.

You co-authored a famous 2007 study "Why Humans Have Sex." Why focus on women this time around?
We discovered that women's sexual psychology turned out to be far more complex than we envisioned. [It] deserved an entire book-length treatment. (See photos: "The Best of the Bond Girls")

What differences between men and women did you notice?
There are important gender differences in sexuality, but these must be interpreted within the context of a high level of similarity. Both women and men have sex because they are physically attracted to the person, for pure pleasure, because they are in love, or simply because they are horny. But within the overall similarity, I'd say women's sexuality tends to be more linked with love and emotional bonding. Women, more than men, like sex when there's some kind of emotional connection. Men were more likely to have sex simply because the opportunity presented itself. Women tend to be pickier, especially for short-term sexual encounters. And men are more motivated to have sex to boost their status among their peers, although some women in our study also had sex for precisely this reason. (Read more about the chemistry of desire.)

What are the main reasons why women have sex?
The most frequent reasons include: sexual attraction to the person, the desire for physical pleasure, to express affection, to express their love for a person or because they were sexually aroused and wanted release.

Other important reasons are to boost their self-esteem or sexual esteem, to get revenge, to secure "mate insurance" in case a partner dumps them, to relieve pain, to achieve health benefits such as getting rid of a headache  yes, it works  to decrease stress, to lose weight and as a sleep aid. We devote one chapter to "sexual economics," which focuses on all the ways in which women have sex as an exchange for other benefits, such as getting her partner to take out the garbage, securing free dinners or getting expensive gifts. We also devote one chapter to what we call "the dark side" of women's sexuality  when women have sex because they were deceived, coerced or forced into it. (See photos: "Same-Sex Overtures Across Species")

Any particularly surprising findings?
I was surprised by the importance of revenge. A few had sex in order to give someone else a sexually transmitted disease. More commonly, women's revenge sex involved getting back at a cheating partner, or having sex with the partner of a friend who had poached her partner. Actually, the frequency of mate-poaching also surprised me  the frequency with which women try to lure men who are already "taken," either for a short-term sexual liaison or a longer-term relationship. Most women have experienced mate-poaching in one form or another, either as the mate poacher or as the victim.

How does evolution explain some of these complexities?
Sexual attraction often boils down to what Darwin called "female choice." Modern women are the descendants of a long and unbroken line of ancestral mothers who made wise sexual choices. As descendants of these successful women, modern women carry with them the sexual psychology  the ancestral wisdom  that led to the success of their female forebears. So women find cues to health, status and protection to be sexually attractive. These are all qualities that led to better survival and reproductive outcomes.(Read about teen girls and sex.)

On the competition side, evolution by selection is an inherently competitive process. It's a cliché that "the good men are all taken, permanent bachelors or gay." And there's some truth to this. The number of truly desirable and available men is limited. So women are in sexual competition with other women for access to the most desirable men. Modern women are the descendants of ancestral mothers who succeeded in besting other women in these sexual competitions.

What physical features do women tend to find most attractive in men?
Body is important to women. Women are sexually attracted to men with a V-shaped torso, or a high shoulder-to-hip ratio, and men who are taller than average. Interestingly, women do not like muscle-bound men, and men misperceive how muscular women want them to be. The face is also critical. A symmetrical face is a health cue, as are a good head of hair and masculine features such a strong jaw and a deep voice. Women generally don't find feminine-looking or feminine-sounding men to be sexually attractive.

What advice could you give to the men out there not blessed with Michael Phelps' torso and George Clooney's face? What can they do to stay in the game?

Have good hygiene. Sense of smell is critical. A man who smells bad, or who has bad breath  that can be a sexual kill switch for women. Interestingly, women have a keener sense of smell than men, so men are sometimes oblivious to how bad they smell to women. A man's scent conveys critical information to women about a man's health status.

The other thing to note about what women find sexually attractive centers on cues that convey personality, sense of humor, self-confidence and social status. These things can transform an average-looking man into a sexually attractive man in the minds of many women.